1. Field of the Invention
The present invention relates to measurement systems. More specifically, the present invention relates to laser-based measurement systems.
2. Description of the Related Art
An antenna array is typically comprised of a plurality of active antenna elements in which the phases of the signals input to the antenna elements can be adjusted to control the directionality of the array. In order for the antenna to deliver good performance, the phase locations of the antenna elements must be known to a small fraction of a wavelength. However, a very large or lightweight structure cannot easily be held to this precision by mechanical means alone. Large antennas, or small but ultra-lightweight antennas, typically flex or distort more than a tenth of a wavelength.
A large space-based radar antenna, for example, may be over 100 meters in length and include a multitude of panels or segments which are joined at their edges by hinges. This hinging arrangement allows the structure to be folded into a compact arrangement for transportation (such as launch to orbit), but also means that there can be a substantial tilt angle between adjacent panels. Each panel may also be subject to deflections or bending due to differential heating, gravity gradients, residual atmospheric drag, and possibly other causes. These deflections and deviations from the ideal need to be precisely measured in order to properly calibrate the antenna array.
Prior approaches to phase calibration of an antenna array include the use of a remote radio frequency calibration source on earth or in co-orbit with the array. This method, however, can have problems with source availability. Alternatively, the array may be calibrated by using a camera that surveys riseau markings on the structure. This technique, however, has resolution limits for very large structures.
Hence, a need exists in the art for an improved system or method for measuring deflections in large structures that offers greater precision than prior approaches.